Mitt Romney escalated the pressure for Donald Trump to release
his tax returns, doubling down on his belief that the presumptive
Republican presidential nominee has something to hide.

"Your imagination can run wild," Romney said in an interview with
CNN's Wolf Blitzer on Friday.

He continued: "He doesn't pay taxes. He doesn't have much
income. He's receiving income from unsavory sources. He has
ownership in enterprises that are perhaps associated with
unsavory enterprises or nations or groups."

Romney, one of the most prominent Republican critics of
Trump, said
in a Facebook post last month that it's "disqualifying"
for presidential candidates not to release their tax
returns, and said that Trump's returns could contain a "bombshell
of unusual size."

He is just one of a growing number of voices calling
on Trump to make his returns public, a tradition observed by
major-party presidential candidates
since the early 1970s.

Trump has resisted the call so far, and Romney said
that "there is no question" that Trump will never come
around.

"There's something in those taxes that's even worse than
shooting someone on Fifth Avenue," Romney said, referencing
a joke Trump made during his primary campaign that he
could shoot somebody in the middle of the street and not lose the
backing of his supporters.

"He will follow one excuse after the other to say why he
can't," he said. "And he'll never release them, because there's
something in there that he feels is worse for him than shooting
someone on Fifth Avenue."

Trump has cited an ongoing IRS audit as the reason why he
has not made his tax returns public.